The present invention relates to hollow railings, bars, grilles, tubes, etc., (hereinafter called "railings"), used as a protection from intruders to commercial buildings, to prevent escape in the case of a jail building, etc.
There are known such railings being provided with an optical fibre or a wire threaded inside through hollow bars connected to discrete sensors and/or to a control and an alarm. Said "alarm" is activated upon cutting of the optical fibre or wire.
The hollow section of these railings are optionally filled with protection material after the optical fibre or wire is inserted.
The known railings are not entirely satisfactory for intrusion detection particularly as they require cutting of the fibre or wire.
It has thus been desirable to develop a railing which overcomes the above drawback. Said railing should be very sensitive to activate the alarm not only while the fibre is cut, but also at an earlier stage or even when the railing is bent without any cutting. Said railing should be easy to manufacture and to mount on the site to be protected.